Scotch broom (Cytisus scoparius) is a Class B Noxious Weed in the state of Washington. Class B means its distribution is limited in the state, something hard to imagine out here on the Olympic Peninsula where it is actually unlimited, and vast swathes of open areas are infested. Broom will take over the lake beds vacated as the Elwha dams come down, despite the effort spent in raising and planting out tens of thousands of native plants as part of the Elwha River restoration.
Speaking of what's hard to imagine, visitors can't believe there's anything at all wrong with scotch broom, because it's gorgeous.
Which is how it got here in the first place: horticulturalists brought it. One website says, "Scotch broom is said to have been introduced to Vancouver Island from Hawaii in the 1850s by Capt. Walter Calhoun Grant who planted it on his farm near Sooke." Another says, "Scotch broom was introduced to California in the 1850s as an ornamental by the nursery industry. It was later used to prevent erosion and stabilize road cuts. Scotch broom is still sold as an ornamental in some regions; this plant will quickly escape cultivation and establish itself in adjacent areas."
I know of at least one person who probably tried to smuggle some home to the far corner of another state, where one has to hope it was unable to thrive...
Oh god. The Noxious Weed Control Board says, "Scotch broom reproduces by seed. Each seed can remain viable for up to 80 years."